1. Field of the Invention
The present invention relates generally to a power steering gear and more particularly to a power steering gear used for reducing steering force without changing the steering gear ratio.
2. Description of the Prior Art
A conventional power steering gear is exemplified by Japanese Utility Model Application Unexamined Open No. Sho. 58-178,061, published Nov. 29, 1983. FIGS. 1 and 2 show the conventional power steering gear disclosed in the above-identified document. The conventional power steering gear comprises: a pipe 14 communicating between a gear housing 6, in which a control valve 10 is incorporated, and a power cylinder 12; and a drive seat 16 interposed between a suction/exhaust port 12a of the power cylinder 12 and the pipe 14. If the diameter of the bore 16a of the drive seat 16 is restricted, a kickback input due to reaction against the road surface is attenuated and vibrations such as steering shimmy, which arises in a specific vehicle speed range, are prevented. In this way, the drive seat functions as an oil damper and prevents noise due to vibrations such as described above. However, since the diameter of the bore 16a of the drive seat 16 is constant in the conventional power steering gear, the line resistance due to the restricted bore 16a of the drive seat 16 is high enough that the steering becomes heavy when high hydraulic pressure is generated in the control valve 10 during abrupt and large steering operations. Consequently, the normal advantages of power steering are not provided during abrupt and large steering operations.